Backpack



FIG. 1 is a front perspective view of the backpack comprising the present invention;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

Broken lines depict portions of the backpack that form no part of the claimed design. 

CLAIM The ornamental design for a backpack, as shown and described. 